1. Field of the Invention
This invention relates to servo motion controls for applying labels to a moving surface and, in particular, to servo systems providing high speed, precise label placement at a desired location on the moving surface.
2. Description of the Prior Art
Servo motors and controls have been applied for some time in high-speed labeling machines such as those disclosed in U.S. Pat. No. 4,294,644 and U.S. Pat No. 4,488,925 wherein a servo motor and servo drive are used to apply labels to a moving surface.
The latter patented device is not able to gradually accelerate or decelerate the label web nor can this device automatically accommodate or track changes in product moving surface speed during application of the label. This device places the labels by causing the labels to start and stop in as short a time as the labeling mechanism will allow. These abrupt starts and stops reduce the accuracy of the label placement, decrease the life of the labeling mechanism, and increase breakage of the label web.
The former patented device, in contrast, does provide gradual acceleration and deceleration of the label web; however, this device does not allow for rapid and convenient adjustment of most of the parameters affecting label placement.
Increasing the speed and accuracy of label placement is a continuing goal because overall production may be constrained by the rate at which labels can be accurately and smoothly applied to the moving surfaces. As a part of speed and accuracy control, it is desirable to provide automatic compensation for web and label stretch or shrinkage and for recovery from a spliced label within one product cycle.
In addition, the control should provide for cycle initiation at a consistent location with respect to the surface on which the label is to be applied, present the label to the surface at a consistent location with respect to the surface and at a consistent velocity with respect to the surface, and maintain that velocity with respect to the surface during the label application.
Furthermore, the control should include the ability to make rapid changes to the labeling machine parameters in order to improve label placement and the capability to make rapid change from one label type to another.
The invention comprises a labeling machine servo motor to drive the label feed in combination with a control system which tracks the surface of the item or part to be labeled and in which all of the parameters affecting the placement of the label are instantly programmable. Label motion starting position, label acceleration and deceleration rates, label speed, and label stop position are all under program control and may be adjusted within the control system or by an external device utilizing a network, a serial interface, or a discrete input/output interface to the control system. In the preferred embodiment, the control system comprises a servo controller easily programmable and reprogrammable in the necessary parameters to effect more accurate and faster label application.